The mechanisms by which infecting viruses regulate the expression of their own genes, and those of the host cell, are being examined in two viral systems - bacteriophage T7 and vaccinia virus. Biochemical and genetic investigations of bacteriophage T7 will be directed at the following areas: 1. Isolation and further characterization of host cells that are resistant to the phage protein kinase (gene 0.7). 2. Examination of the role of gene 1.1 in the shut-off of host macromolecular synthesis in T7-infected male strains of E. coli. 3. Studies of the structural and functional stability of the early and late classes of phage mRNA. We will continue to study the transcription in vitro by vaccinia virus core particles. We intend to compare the spectrum of products synthesized by core particles prepared in a number of different ways to the pattern observed in vivo at early times after infection.